The cylinder block has a corresponding number of cylinder bores for receiving the pistons. The piston serves to transmit the gas forces which are generated by the combustion to the crankshaft. For this purpose, the piston is connected in an articulated manner to the crankshaft by a connecting rod.
The cylinder head usually serves to receive the air and fuel and to exhaust the spent gases after combustion. In four stroke engines, almost exclusively poppet valves are used to control the gas exchange, which poppet valves perform an oscillating reciprocal movement during the operation of the internal combustion engine, opening and closing the intake and the exhaust ports. At least a portion of the intake and exhaust channels is integrated into the cylinder head.
The design of the cylinder head is influenced greatly by the components and elements which are required for the gas exchange: both in providing the gas channels and the valve timing mechanism for actuating and controlling the intake and exhaust valves.
For example, the generation of what is known as a tumble or a swirling flow can accelerate and assist the mixture formation. A tumble is an air eddy about an imaginary axis extending roughly parallel to the axis of the crankshaft, in contrast to swirl which represents an air eddy extending parallel to the axis of the cylinder.
The problems with regard to the very limited installation space in and on the cylinder head are increased by the fact that modern designs for internal combustion engines provide four or five valves per cylinder, which requires or necessitates a corresponding number of cylinder openings and gas exchange channels.
In addition, in spark ignition internal combustion engines, the required ignition apparatus and, moreover, in particular in the case of direct injection internal combustion engines, injector are to be arranged in the cylinder head. For this purpose, the required installation space not only has to be provided, but to optimize the mixture formation and the combustion process, a defined arrangement of the ignition apparatus and the injection device in the combustion chamber is desired.
Therefore, in direct injection internal combustion engines, an injection jet which is directed counter to the tumble can be expedient to distribute the fuel in the entire combustion chamber. This presupposes corresponding positioning of the injection nozzle.
If the internal combustion engine is liquid cooled, a plurality of coolant channels are provided in the cylinder head, which coolant channels guide the coolant through the cylinder head. The arrangement of coolant channels leads to an extremely complex structure of the cylinder head construction. The cylinder head is subjected to high mechanical and thermal loads which weaken its strength by the introduction of the coolant channels. Because the energy is conducted to the cylinder head surface before being dissipated, the coolant channels are designed to guide the coolant flow as close as possible to those regions of the cylinder head which are subjected to high thermal loads, i.e., in the vicinity of the combustion chamber
In small, highly pressure-charged engines, liquid cooling is of even greater importance than in conventional internal combustion engines.
To connect the cylinder head to the cylinder block, bores are provided both in the cylinder head and in the cylinder block, the cylinder block and the cylinder head being arranged for assembly with respect to one another in such a way that the bores are aligned with one another. Typically, a gasket is placed in between the block and the head to achieve reliable sealing of the combustion chambers. The cylinder head is connected to the cylinder block by threaded bolts which are introduced into the bores of the cylinder head and the cylinder block and are tightened. Typically, there are four bolts around each cylinder.
Typically, the cylinder head is a cast part; thus, aspects which relate to casting technology also have to be considered during the design and production. For example, the cylinder head wall thickness should vary only slightly and not suddenly. Sharp-edged transitions are to be avoided and a minimum wall thickness is to be maintained.
The development toward more compact cylinder heads is also motivated or driven by the fact that internal combustion engines are increasingly equipped with a pressure-charging device, i.e., a supercharger or a turbocharger. The pressure-charging device provides increased power output with an unchanged displacement or allows a displacement reduction with the same power output, i.e., downsizing.
To package the engine, particularly when the bore diameters and bore spacing is smaller challenges the designer to provide all of the functions described above as well as maintain a cost-effective design.
According to one approach, the various components to be integrated into the cylinder head are combined. German laid-open publication DE 37 31 211 A1 (equivalent to U.S. Pat. No. 4,967,708) describes, for example, a fuel injection valve configured integrally with an ignition apparatus, forming one contiguous, compact component. As a result, the number of components to be arranged in the cylinder head is reduced and the installation space required by these components is reduced.
However, a combined ignition/injection device of this type is an expensive component. Secondly, a close arrangement of this type of the ignition apparatus and the injection device is also not desirable in all applications. The ignition apparatus and the injection device are optionally to be arranged spaced apart from one another in the cylinder head.
German laid-open publication DE 197 53 965 A1 (equivalent to EP 921289 B1) describes an internal combustion engine in which the injection valve extends substantially within the intake channel, to reduce the required installation space, and in the process is arranged next to the intake valve. This is also intended to be advantageous because the injection valve is cooled by the fresh air which is sucked in as a consequence of the arrangement in the channel. However, this advantage largely disappears when high rates of exhaust gases are recirculated into the intake. Furthermore, the gas exchange is influenced in an uncontrolled manner by the placement of the injection valve in the intake channel. The introduction of the valve into the channel also requires sealing of the valve with respect to the channel, to prevent fresh air or fresh mixture escaping out of the intake channel into the surroundings.